linux-kernel - Re: [PATCH v3 1/3] tracing: Show real address for trace event arguments

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Date:   Tue, 20 Apr 2021 12:16:47 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     Masami Hiramatsu <mhiramat@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] tracing: Show real address for trace event
 arguments


On 19/04/2021 19:22, Steven Rostedt wrote:
> On Mon, 19 Apr 2021 14:08:14 +0100
> Jon Hunter <jonathanh@...dia.com> wrote:
> 
>> I have encountered the following crash on a couple of our ARM64 Jetson
>> platforms and bisect is pointing to this change. The crash I am seeing
>> is on boot when I am directing the trace prints to the console by adding
>> 'tp_printk trace_event="cpu_frequency,cpu_frequency_limits"' to the
>> kernel command line and enabling CONFIG_BOOTTIME_TRACING. Reverting this
>> change does fix the problem. Let me know if you have any thoughts.
> 
> Thanks for the report. I was able to reproduce this on x86 as well.
> 
> It's the tp_printk that's the problem. Does this fix it for you?
> 
> -- Steve
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 66a4ad93b5e9..f1ce4be7a499 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3580,7 +3580,11 @@ static char *trace_iter_expand_format(struct trace_iterator *iter)
>  {
>  	char *tmp;
>  
> -	if (iter->fmt == static_fmt_buf)
> +	/*
> +	 * iter->tr is NULL when used with tp_printk, which makes
> +	 * this get called where it is not safe to call krealloc().
> +	 */
> +	if (!iter->tr || iter->fmt == static_fmt_buf)
>  		return NULL;
>  
>  	tmp = krealloc(iter->fmt, iter->fmt_size + STATIC_FMT_BUF_SIZE,
> @@ -3799,7 +3803,7 @@ const char *trace_event_format(struct trace_iterator *iter, const char *fmt)
>  	if (WARN_ON_ONCE(!fmt))
>  		return fmt;
>  
> -	if (iter->tr->trace_flags & TRACE_ITER_HASH_PTR)
> +	if (!iter->tr || iter->tr->trace_flags & TRACE_ITER_HASH_PTR)
>  		return fmt;
>  
>  	p = fmt;
> @@ -9931,7 +9935,7 @@ void __init early_trace_init(void)
>  {
>  	if (tracepoint_printk) {
>  		tracepoint_print_iter =
> -			kmalloc(sizeof(*tracepoint_print_iter), GFP_KERNEL);
> +			kzalloc(sizeof(*tracepoint_print_iter), GFP_KERNEL);
>  		if (MEM_FAIL(!tracepoint_print_iter,
>  			     "Failed to allocate trace iterator\n"))
>  			tracepoint_printk = 0;
> 


Yes that works for me thanks!

Tested-by: Jon Hunter <jonathanh@...dia.com>

Cheers!
Jon

-- 
nvpublic